


Tomorrow Past Tonight

by moneychangeseverything



Category: The Transformers (Cartoon Generation One), Transformers - All Media Types
Genre: Banter, First Time, First Time Blow Jobs, Gift Fic, Interfacing Mods, M/M, Smut, Sticky Sexual Interfacing, Sunstreaker POV, Tracks is mentioned, Twincest, robot medical procedures
Language: English
Status: Completed
Published: 2020-12-27
Updated: 2020-12-27
Packaged: 2021-03-11 03:08:20
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 2,847
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28368159
Author URL: https://archiveofourown.org/users/moneychangeseverything/pseuds/moneychangeseverything
Summary: “Primus, Sides! You’re so embarrassing,” Sunstreaker hissed.“I’m not wrong, though,” Sideswipe replied, lowering his voice apologetically.“Whatever, you’re the one who cares about interfacing, not me,” Sunstreaker sighed. “And I hope you have enough shanix to pay for the mod, because I am not spotting you this time.”
Relationships: Sideswipe/Sunstreaker (Transformers)
Comments: 6
Kudos: 28
Collections: Secret Spark Exchange 2020





	Tomorrow Past Tonight

**Author's Note:**

  * For [Kess](https://archiveofourown.org/users/Kess/gifts).



> A holiday gift fic for Lofi!!   
> cw: contains teenage Sideswipe and Sunstreaker (Cybertronian equivalent of sixteen or seventeen), and explicit sticky between the twins, as well as minor robot medical procedures and brief worries that someone is injured - let me know if you need more info about any of this.

“Look, Sunny, it’ll be fun!” Sideswipe insisted. 

“Sitting around in a waiting room for half a day? Yeah, sounds like a real blast,” Sunstreaker snorted. 

“C’mon, you’re not going to let Tracks win, are you?” Sideswipe wheedled. 

“You’re the one he dared, Sides, not me.” 

“Yeah, but we’re basically the same person, so - please?” 

Slaggit. Sunsreaker was always weak to those big, shining optics. Sideswipe was just so fragging cute, the childish curves of his cheeks starting to thin out, revealing sharp cheek struts as he grew into his face. Every day it felt like the two of them woke up looking different - their youth growth spurt was fragging annoying sometimes, but Sunstreaker had to admit that he liked seeing the changes in Sideswipe’s frame. 

Well, of course his twin looked good - he looked just like Sunstreaker, who was nothing less than a work of art at all times. So yeah, he was going to give in. But that didn’t mean he wouldn’t let his brother sweat for another minute or two. 

He waited until Sideswipe’s grin started to wobble before sighing. “Fine, Sides. I’ll go with you.” 

Sideswipe threw his arms around his golden twin with a laugh. “I never doubted you, Sunny!” 

“Don’t call me that!” 

“Whatever. So c’mon - let’s go to the mod shop.” 

“What, right now?” Sunstreaker asked, even as he started walking. 

“Yeah! No time like the present, right? Tracks definitely won’t expect us to have it done when we show up at class tomorrow.” 

“Woah, Sides. What’s this us?” 

“Me. I meant me! But - if you wanted to?” Sideswipe trailed off. 

“I don’t. You might think that replacing your transfluid reservoir will get you laid, but I’m pretty sure that Tracks is making that up,” Sunstreaker grumbled. 

“He lives in the Towers, Sunny! He knows how people do things - and by things I mean _sex things_. He told me that his brother’s friend touched his spike.” 

“I know, Sides, you’ve told me that like ten times. And I’m here to say again, so what?” 

“So, that’s one more person than you’ve had touch your spike, Sunny!” 

Sunstreaker cringed at his twin’s volume - they were elbowing their way through the crowded commercial districts now, almost at the mod shop, and more than a few bots turned to stare at the kid shouting about his spike in the middle of the street. 

“Primus, Sides! You’re so embarrassing,” Sunstreaker hissed. 

“I’m not wrong, though,” Sideswipe replied, lowering his voice apologetically. 

“Whatever, you’re the one who cares about interfacing, not me,” Sunstreaker sighed. “And I hope you have enough shanix to pay for the mod, because I am not spotting you this time.” 

Sideswipe just grinned and danced through the door. 

Sunstreaker followed his brother with significantly less pep in his step - Sideswipe was already leaning on the counter, flirting with the clerk by the time he got inside. 

“- so then I said - actually, sorry babe, maybe that’s a story for another time? I’d love to spend all day chatting with you, but I gotta get in and get out if you know what I’m saying.” Sideswipe followed his patter with an outrageous wink, and the idiot behind the till actually blushed. Sunstreaker’s brother was becoming more trouble every day. 

Before he could try to get the conversation back on track, another bot walked out from the back of the shop - an absolutely beautiful bot. Normally, that wouldn’t phase Sunstreaker - not many people looked better than himself, and between him and Sideswipe, they could out-beautiful most mechs. But this bot was an exception. Wicked curves, deliciously wet-looking cherry red plating, and little hints of gold that just drew the eye - Primus! Sunstreaker could feel his whole frame heating up. 

It was ridiculous. Sunstreaker never reacted like this. Hell, he had red and pretty staring him in the face every day. But there was just something about this mech’s perfect finish that had his mouth watering. It was nothing like the scuffs and streaks of Sideswipe’s friends, or even the overpriced perfumed wax that Tracks loved to brag about so much. This mech’s plating was practically glowing from within. Sunstreaker didn’t know if he wanted to beg for his secrets, or wilt from embarrassment at how shoddy he looked in comparison. 

He finally dragged his gaze up to the mech’s face, only to find him looking right back at Sunstreaker with a bemused smile. 

“Hey kid,” he said, “what can I do for you today?” 

“Oh! Um,” Sunstreaker stuttered, embarrassingly. “We’re here for a transfluid reservoir upgrade?” 

“Sure thing, kid. It’s a good first mod to start off with, if you ask me. Why don’t you and your friend come on back here, and we’ll figure out how much it’ll be.” 

Sunstreaker trailed after the lovely mod-tech, ignoring Sideswipe’s intense smirking. Those swaying hips led him and his twin to a small room, where they sat down side-by-side on the med-berth. 

“I’m Knock Out, by the way,” the cherry racer said, settling onto the wheeled stool and smiling up at them. Sunstreaker barely held back the _you sure are_ that jumped to his lips. Knock Out probably got that all the time - he didn’t need to embarrass himself any more than he already had. 

“I’m Sideswipe, and this golden idiot here is my brother, Sunstreaker,” Sides said, as effortlessly charming as ever. His twin had never lacked for confidence - apparently not even when talking to a bot who was better looking than the Prime himself. 

“Lovely to meet you. And what are we thinking for the transfluid tanks today?” 

“Well, I’m hoping to change the colour nanites for sure, and I was thinking maybe a little volume increase. Nothing crazy, but maybe an extra quarter-astroliter or so?”

How was Sideswipe so good at this? He really sounded like he knew what he was talking about. Maybe Sunstreaker should give his brother a little more credit, next time. 

“I do wanna be able to come into a cube of energon from half a room away, though. So like, enough for that.” 

Or maybe not. Sunstreaker knew that if Sides had his way, he’d be the aft holding the cube of energon - and that thought was enough to snap him out of his half-embarrassed and half-lustful haze. 

“No. Absolutely not,” he snapped. “Colour nanites and a ten percent volume increase, tops.” 

“Alright, colour and ten percent for both of you sounds do-able. I assume you’d like the transfluid to match your plating? That is a rather lovely shade of gold,” Knock Out said, pulling out a datapad and starting to input information. 

Sunstreaker felt his face flame in blush hotter than the surface of the sun, and was once again too tongue-tied to answer. 

“Yeah, that’s what I was thinking, but now - I dunno. What do you think of switching, Sunny? I could have the gold, and you could have some nice cherry red?” Sideswipe leaned into his shoulder with another wink. 

Cherry red. Sideswipe’s red was more of a fire engine red, a red like the hot glow of molten metal, leaning towards oranges rather than pinks. No, cherry red more accurately described the delicious medic who was sitting before them - long, shapely legs crossed, with one golden-wheeled pede tapping. 

Yeah, Sunstreaker was still blushing. He managed a shrug. 

“Sure, I can do that for you,” Knock Out said, tone businesslike. He was either oblivious to Sunstreaker’s crush-at-first-sight, or just used to having that effect on bots. Probably the latter, honestly. 

“Great!” Sideswipe enthused, kicking his pedes against the side of the med-berth.

“Here,” Knock Out handed over the datapad. “Take a look at these specs and the quote, and pick from the colour options. Once you’ve paid, we can get started with the procedure.” 

Sunstreaker accepted the datapad - not a chance in the Pit he was letting Sideswipe have the final say on colours - and nodded as the medic left the room. 

As the door clicked shut, Sideswipe turned to his twin with a slag-eating grin. “You liked him, huh?” 

“He seems like a competent mod-tech,” Sunstreaker muttered. 

“Sure, and that’s why you spent the last ten kliks thinking about how you wanted to lick his plating?” 

“Shut up and fill out the form!” 

\-- 

The procedure was surprisingly quick and painless, but Sunstreaker felt a little woozy as he sat up on the med-berth and looked at Knock Out’s gorgeous red optics. 

“Everything looks good,” the medic said warmly. “Make sure you take it easy for the rest of the day while the parts integrate. Tonight you’re going to want to clean out the pipes a couple of times, but don’t go crazy - you need to leave enough nanites in there to set up a sustainable population, okay?” 

“Um, okay?” Sunstreaker replied. 

“Yeah, no worries doc, we’ve got this,” Sideswipe said. 

“Great. Call the clinic if you have any serious pain or bleeding - but you won’t, so don’t worry,” Knock Out smiled, patted Sunstreaker lightly on the shoulder, and walked out of the room. 

“You even let him touch you?” Sideswipe asked. He was still smirking, but there was something a little brittle about the expression - the suppressed hilarity from earlier was gone. 

“He just had his hands all over both of our internals,” Sunstreaker pointed out. 

“That’s different and you know it,” Sideswipe said quietly, getting to his feet. 

Sunstreaker sighed and wobbled up from the berth, slinging an arm around his brother. “Let’s go home, Sides.” 

Sideswipe didn’t reply, but he did wrap an arm around his twin’s waist, taking his weight and steadying him as they walked out into the street. 

Sunstreaker was glad that their dorm room wasn’t far - his internals felt weird, with a hot and heavy sense of pressure sitting low in his belly, sending flashes of something sparkling and strange through his legs and core as he walked. He felt warm, too, like the blush of being around Knock Out had taken up residence in his frame. It wasn’t exactly painful, but he was in no mood to be out in public, brushing against strange bots. Sunstreaker wanted to be in his berth, curled up safe with Sideswipe, under the covers. 

He gritted his dentae and kept walking, clinging to his brother a little more tightly. 

“You alright, Sunny?” Sideswipe asked quietly. 

“Just feel a bit weird, that’s all,” Sunstreaker admitted.

“You’re not bleeding or anything, are you?” Sideswipe’s voice was rigidly calm, the way it always got when he was trying not to panic. 

“No, I don’t think so.” 

“Well, we’re almost home, okay?” 

Sideswipe was right - he could see the door of their habsuite now. He hung on while his brother keyed open the cheap lock, and then carefully limped inside. 

“Okay, sit on the berth, Sunny - let me look.” 

He did, leaning back and splaying his golden legs open, looking for tell-tale trickles of energon or swollen cables. 

“I don’t see anything, Sides,” Sunstreaker said. 

“No, I don’t either,” Sideswipe agreed, gently pressing his abdomen. It didn’t feel _bad_ , just strange - Sunstreaker bit his lip to keep from letting out a gasp. 

“Open your panel for me, Sunny?” Sideswipe still looked worried, but the panic in his eyes was starting to ease. Sunstreaker shifted a little awkwardly, but sent the command to open his modesty panel so they could both look. 

As soon as the cover snapped back, Sunstreaker’s spike pressurized, rising up between them with shimmering red transfluid already beading on the tip. He squirmed as Sideswipe delicately pressed at the base. 

“Does that hurt?” the red twin asked. 

“N-no.” 

“Sunny,” Sideswipe looked up at his brother’s face, a little grin starting to pull up the corners of his lips. “Can you explain what you meant when you told me you felt weird?” 

“I - I just feel hot, I don’t know. There’s a weird pressure in my abdomen, I feel like I can’t sit still,” Sunstreaker stuttered. Sides still had one hand around the base of his spike, and the other resting on his inner thigh. As hot as Sunstreaker’s plating felt, Sides’ hands were hotter, practically burning. Sunstreaker gave in to the urge to squirm a little more. 

“Sunny, babe,” Sideswipe started, smiling for real now. “Do you remember when Knock Out said we’d need to clean out the pipes tonight?” 

The thought of Knock Out’s sharp porcelain faceplate raised Sunstreaker’s core temperature another couple notches. But - “I thought he meant like, wash off in the washracks?” 

“Ah, no. It was one of those, what do you call them? Euphemisms.” 

“Oh.” Sunstreaker was distantly impressed that Sideswipe remembered the word, but the rising tide of heat in his frame was making it difficult to think. “Euphemism for what?” 

“For overloading, Sunny,” Sideswipe said gently. “Self-servicing, mainly.” 

“Oh,” Sunstreaker said. Sideswipe wasn’t letting go of his spike - instead he was holding it a little more tightly, wrapping his fingers around the shaft. Sunstreaker felt like he was about to combust. 

“You’re feeling weird because you’re charged up, Sunny. Your system wants to get rid of the excess transfluid by overloading, that’s all.” Sideswipe was still smiling up at him from where he was kneeling on the floor, looking totally at ease between Sunstreaker’s spread legs. 

“Oh,” he said. If he had a few more thoughts in his helm, he might feel a little embarrassed at sounding like a broken record. Right now, though, he was a lot more focused on the feeling of his brother’s hand starting to stroke his spike, fingers slipping over the head and the back down with perfect tightness. His eyes were caught by the sight of Sideswipe’s tongue darting out to lick his lips. 

Sunstreaker let himself gasp, fans clicking on. “Wha-what should I do, Sides?” he asked.

“Nothing, baby,” Sideswipe murmured, leaning a little closer. “Just sit back and let me take care of you.” His hand was still stroking Sunstreaker’s spike, perfectly tight and hot. 

Sitting back suited Sunstreaker just fine - he felt perfect right now, all that strange heat concentrating deep in his belly, pulsing in time to the rhythm of Sideswipe’s servo. He leaned back on his hands, thrusting his hips up into his brother’s grasp, trying to get a little more of the delicious sensation. 

Sideswipe gave a breathless laugh, easily adjusting to meet his twin’s thrusts. “What happened to all those times you told me self-servicing was gross, huh?” he asked. 

“It is gross when you get transfluid all over my - oh frag! - my good polishing cloths,” Sunstreaker whined. 

“Mmm, you’re the one getting ‘fluid everywhere right now, baby,” Sideswipe laughed, smearing the bright red pre-come over the hot golden spike in his hand. 

“Maybe you should - oh! - do something about that, Sides.” Sunstreaker wasn’t sure exactly what he was implying - Sides wasn’t kidding when he teased his brother about being uninterested in interfacing, he’d really never seen the appeal until now - but he liked the hot look that came into his twin’s bright blue optics. 

“Maybe I will,” Sideswipe smirked, leaning in and _licking_ the head of Sunstreaker’s spike. 

Sunstreaker gasped, with almost more shock than lust. Sideswipe’s tongue was hot, slick - electric on his oversensitized cable. It felt almost impossibly good. 

“More, please Sides,” he begged shamelessly. 

“Shh, don’t worry Sunny. I said I’d take care of you, didn’t I?” Sideswipe ducked back down, sucking the whole head of his twin’s spike into his mouth. 

Sunstreaker moaned loud enough to rattle the window in its frame. Primus, that was amazing - the heat, the suction, the slick bobbing of Sides’ lips and the stroke of his tongue! Sunstreaker led his head loll back on his shoulders, offlining his optics. The visual of his brother’s gorgeous mouth stretched around his spike was just too much - if he’d been ready to combust before, now he was bursting into flames. 

He thrust lightly into Sideswipe’s mouth a few more times, but everything was too perfect. Too tight, too hot - he couldn’t hang on. Sunstreaker felt the intense sensation peak impossibly higher, concentrating somewhere deep inside him, then shooting out in a blinding overload. 

He collapsed back onto the berth, gasping for a vent of cool air. Sideswipe stayed kneeling on the ground for a minute, gagging and swallowing, before laying down next to him and wrapping his arms around his twin. 

“You were right, Sunny,” he muttered, “that ten percent increase was more than enough.” 

Sunstreaker managed to roll his head to the side and open an optic to look at Sideswipe - grinning like a fool with red transfluid all over his lips. 

“Isn’t it your turn to clean the pipes, now?” he asked. 

“Mm, y’know, I think it is,” Sideswipe agreed. “Maybe I’ll cover you in some of this lovely gold transfluid to remind you who you belong to.” 

Sunstreaker leaned in, kissing his brother slowly before licking his face clean. 

“I already know I’m yours, Sides,” he said. “But if you want to, I guess I could deal with that.” 

Sideswipe laughed, panel already snapping open as he rolled on top of his twin.

**Author's Note:**

> And then later they go back to the clinic and have a threesome with Knock Out.   
> Thanks for reading and merry December, please leave some feedback if you'd like!


End file.
